IBS doesn't have anything to do with how healthy you are (but bad health can make it worse), so I believe you can get it.
Stress can IBS worse, and running makes you feel better, so if you can handle it, it might be a good idea to keep doing that.
Next time you see your doctor, ask them why you can't run, how it makes it worse. That's an easier way to get your answer.
You can have IBS at any age. Some are even born with IBS. I had it when I was your age, even though I didn't get diagnosed 'til years later. Exercise is actually encouraged, so there really is no reason to not run track and field.
Stress can IBS worse, and running makes you feel better, so if you can handle it, it might be a good idea to keep doing that.
Next time you see your doctor, ask them why you can't run, how it makes it worse. That's an easier way to get your answer.